MAXI J1727-203 Transition to the Hard State

ATel #11881; John Tomsick (SSL/UCB), Aarran Shaw (U. Alberta), Javier Garcia (Caltech), Dom Walton (Cambridge), Felix Fuerst (ESAC), Jon Miller (Univ. of Michigan), Michael Parker (ESAC), Yanjun Xu (Caltech)
on 22 Jul 2018; 18:33 UT
Credential Certification: John A. Tomsick (jtomsick@ssl.berkeley.edu)

Tweet

The black hole candidate X-ray transient MAXI J1727-203 was discovered on 2018 June 5 (Yoneyama et al., ATEL#11683). The source quickly made a transition to a soft or intermediate state (Negoro et al., ATEL#11696). NICER measurements on June 5th showed a thermal component with kT near 0.2 keV along with a power-law component with a photon index near Gamma = 2.5 (Ludlam et al., ATEL#11689). A Swift/XRT measurement on June 7th (Kennea et al., ATEL#11697) showed a similar photon index but a hotter thermal component (kT = 0.46+/-0.01 keV). The highest flux reported was 3.9e-9 erg/cm2/s (0.5-10 keV, absorbed) from the Swift/XRT observation (ATEL#11697). Based on an inspection of the MAXI light curve and our analysis of Swift/XRT observations on June 9, 13, and 16, kT peaked near 0.56+/-0.01 keV, and the 0.5-10 keV absorbed flux peaked near 7.3e-9 erg/cm2/s (based on the June 13 measurements).

The Swift/XRT monitoring restarted in mid-July, and observations were made on July 10, 13, 16, 19, and 22. The observation on June 16 had no usable data due to a mispointing of the satellite, but we analyzed the data from the other four observations. We modeled the 0.5-10 keV spectra with an absorbed disk-blackbody plus power-law model. The column density measurements ranged from (3.6+/-1.1)e21 atoms/cm2 to (5.2+/-0.6)e21 atoms/cm2. On July 10, the disk temperature was 0.18+/-0.01 keV, and it was 0.14-0.15 keV for the other three observations (July 13, 19, and 22). A gradual hardening of the power-law photon index is observed: Gamma = 2.04+/-0.06 (July 10), Gamma = 1.97+/-0.06 (July 13), Gamma = 1.85+0.07-0.03 (July 19), and Gamma = 1.75+/-0.08 (July 22). Over the same time, the 0.5-10 keV absorbed flux drops from 1.37e-9 erg/cm2/s to 6.1e-10 erg/cm2/s. The change in the photon index shows that the source is entering or has entered the hard state.

A NuSTAR TOO has been approved for the coming week and is being scheduled. It will most likely occur on July 24 or 27. See http://www.srl.caltech.edu/NuSTAR_Public/NuSTAROperationSite/Schedule.php for updates on the schedule. Coordinated observations are encouraged.